PCI card - finding the voltages used

1. Introduction

The design of the PCI bus places a number of voltages in the bus connector. A PCI card may use one, multiple or all of the voltages provided . As a minimum all of the PCI cards use +3.3V and/or +5V power. Depending on the functions of the card and the way they are realized, the PCI card may use other voltages as well.

This article will give you a practical way of recognizing what voltages a PCI card is using and what is necessary to make the PCI card function on one of the SSI2, or XPRS families of cards.

2. Voltages on the PCI bus

There are the four voltages provided for use on the PCI bus: +3.3V , +5V , +12V , -12V. The maximum currents defined in the speck are: +3.3V/7.6A , +5V/5A , +12V/500mA , -12V/100mA. Full details on the PCI bus are available on -
Wikipedia, and
TechFest.

The PCI bus defines 'component' side of the PCI card as - side B (the above image), and 'solder' side - as side A (image below).

The specification defines 'keying' - openings on the bus side of the pc board. Based on the location of the openings, there are 3 types of boards: '5V card', '3.3V card', and 'universal (3.3V and 5v) card'.

The 2 images show 3 PCI cards, each one is 32bit, and one of them is '5V card', and the other 2 are - 'universal (3.3V and 5V) cards'.

Regardless of the 'keying' of a card, it may use both 3.3V and 5V voltages, even when defined as a 3.3V or 5V type of a card.

The power supplying pins for the optional +12V and -12V voltages are located on:

side A - starting from the right to left: pin1 = ......., pin2 = +12V, pin3 = ...

There are the following scenarios for powering -
- use 'pwr-5v' - PCI card-s using only 3.3/5v
- or, use 'pwr-5v' and 'isa-pwr' - PCI card-s using 3.3/5v, and +12v,-12v low current
- or, use 'isa-pwr-xr' - PCI card-s using 3.3/5v, and +12v,-12v high current

3. Examples

3.1. PCI card - need of +12V and -12V

The PCI card in the picture below needs both optional voltages.

Going through the pins reveals that - sideB/pin1=-12V (left image), and sideA/pin2=+12V (right image) are both connected/used. There are thick lines going up to the components on the circuit board .

3.3. PCI - need of +12V

The PCI card in the pictures below need only one of the optional voltages.

Going through the pins reveals that sideB/pin1=-12V (left image) is not connected/used. However sideA/pin2=+12V (right image) is connected/used - there is a thick line going up to the components on the circuit board .